Plasma induced flow control of boundary layer at airfoil endwall

Abstract

Plasma generators ( 48, 49, 70, 71 ) in an endwall ( 25 ) of an airfoil ( 22 ) induce aerodynamic flows in directions ( 50 ) that modify streamlines ( 47 ) of the endwall boundary layer toward a streamline geometry ( 46 ) of a midspan region of the airfoil. This reduces vortices ( 42 ) generated by the momentum deficit of the boundary layer, increasing aerodynamic efficiency. The plasma generators may be arrayed around the leading edge as well as between two airfoils ( 22 ) in a gas turbine nozzle structure, and may be positioned at correction points ( 68 ) in streamlines caused by surface contouring ( 66 ) of the endwall. The plasma generators may be oriented to generate flow vectors ( 74 ) that combine with boundary layer flow vectors ( 72 ) to produce resultant flow vectors ( 76 ) in directions that reduce turbulence.

The invention claimed is: 
     
       1. An apparatus comprising:
 an airfoil comprising a leading edge, a trailing edge, a pressure surface between the leading and trailing edges, a suction surface between the leading and trailing edges opposite the pressure surface, and a span of the airfoil between opposed ends of the airfoil; 
 an endwall at one end of the airfoil and generally transverse to the span of the airfoil; and 
 a plasma generator disposed on the endwall and effective to accelerate a boundary layer flow over the endwall toward a direction of a streamline pattern existing proximate a mid-span of the airfoil. 
 
     
     
       2. The apparatus of  claim 1  wherein the plasma generator is elongated in a direction that radiates from an intersection between the airfoil and the endwall, and the plasma generator urges the flow substantially parallel to the intersection. 
     
     
       3. The apparatus of  claim 1  wherein the endwall comprises a curved surface with variations in height in a direction of the span, including a relative peak proximate a pressure side of the leading edge of the airfoil and a relative valley proximate a suction side of an adjacent airfoil, wherein the curved surface deflects a boundary layer streamline toward a direction of a corresponding mid-span streamline, and wherein the plasma generator conforms in shape to the curved surface. 
     
     
       4. The apparatus of  claim 3  wherein the plasma generator is located proximate a correction point where the boundary layer streamline is first diverted by the curved surface toward the direction of the corresponding mid-span streamline. 
     
     
       5. The apparatus of  claim 1  wherein the plasma generator comprises two electrodes separated by a dielectric material, and the plasma generator is formed by layering in a thermal barrier coating on the endwall, with the thermal barrier coating being the dielectric material. 
     
     
       6. The apparatus of  claim 1 , further comprising the plasma generator being disposed proximate a throat region defined between the airfoil and an adjacent airfoil. 
     
     
       7. The apparatus of  claim 1 , further comprising a plurality of plasma generators disposed on the endwall and effective to influence the aerodynamic boundary layer flow over the endwall at a respective plurality of locations along its passage from the leading edge to the trailing edge. 
     
     
       8. The apparatus of  claim 1 , wherein the plasma generator is angled to produce a flow acceleration vector that produces a resultant boundary layer flow vector at an angle between a boundary layer flow vector and the acceleration vector, wherein the resultant flow vector is in the direction of the mid-span streamline pattern. 
     
     
       9. The apparatus of  claim 1 , wherein the plasma generator comprises a row of smaller plasma generators, wherein each of the smaller plasma generators is angled to accelerate a boundary layer flow to produce a resultant boundary layer flow in a direction and increased speed that reduces turbulence. 
     
     
       10. An apparatus comprising:
 first and second airfoils spanning between two endwalls; 
 each airfoil comprising a leading edge, a trailing edge, a pressure surface between the leading and trailing edges, a suction surface between the leading and trailing edges opposite the pressure surface, and a span of the airfoil between the endwalls; and 
 a plurality of plasma generators on at least one of the endwalls that accelerate an aerodynamic boundary layer of said one endwall toward being parallel to a 2D aerodynamic streamline geometry defined in a plane transverse to the airfoils at a midspan region of the airfoils. 
 
     
     
       11. The apparatus of  claim 10  wherein said at least one endwall comprises a curved surface with variations in height in a direction of the span, including a relative peak proximate a pressure side of the first airfoil and a relative valley proximate a suction side of the second airfoil, wherein the curved surface deflects a boundary layer streamline toward a direction of the 2D streamline geometry, and wherein at least some of the plasma generators conform in shape to the curved surface. 
     
     
       12. The apparatus of  claim 11  wherein at least one of the plasma generators is located at a correction point caused by the curved surface of the endwall where the boundary layer streamline is first diverted toward direction of the 2D streamline geometry by the curved surface. 
     
     
       13. The apparatus of  claim 10  wherein each plasma generator comprises two electrodes separated by a dielectric material, and at least some of the plasma generators are formed by layering in a thermal barrier coating on said at least one endwall and use the thermal barrier coating as the dielectric material. 
     
     
       14. The apparatus of  claim 10  wherein the two airfoils and the two endwalls form a turbine nozzle. 
     
     
       15. The apparatus of  claim 10  wherein at least one of the plasma generators is mounted across a minimum throat area of a gas flow path between the two airfoils. 
     
     
       16. An apparatus comprising:
 a pair of airfoils and an endwall there between defining an air passage for the flow of a fluid, the air passage comprising an upstream half and a downstream half; 
 a boundary layer of the fluid flow proximate the endwall creating a horseshoe vortex in the fluid flow migrating from proximate a pressure side of a first of the airfoils in the upstream half to a suction side of a second of the airfoils in the downstream half; 
 structure disposed in the endwall in both the upstream half and the downstream half of the air passage, the structure comprising 
 a) contouring on the endwall between the airfoils, and 
 b) a plasma generator in the endwall in the air passage; 
 wherein the structure redirects the horseshoe vortex away from a trailing edge of the second of the airfoils. 
 
     
     
       17. The apparatus of  claim 16 , wherein the structure comprises a curved surface of the endwall in the upstream half and a plasma generator disposed in the endwall in the downstream half. 
     
     
       18. The apparatus of  claim 17 , wherein the plasma generator is disposed at a throat region defined between the airfoils. 
     
     
       19. The apparatus of  claim 16 , wherein the plasma generator is disposed proximate a leading edge of the first airfoil at a streamline correction point where the contouring first redirects a streamline in a boundary layer flow to redirect the horseshoe vortex. 
     
     
       20. The apparatus of  claim 19 , wherein a peak of the contouring is proximate the leading edge of the first airfoil, and further comprising a second plasma generator that spans from the pressure side of the first airfoil to a suction side of the second airfoil across a throat region defined at a minimum separation between the airfoils.